RFR: 8324433: Introduce a way to determine if an expression is evaluated as a constant by the Jit compiler [v5]

[Aleksey Shipilev]

On Tue, 23 Jan 2024 17:21:47 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Hi,
>> 
>> This patch introduces `JitCompiler::isConstantExpression` which can be used to statically determine whether an expression has been constant-folded by the Jit compiler, leading to more constant-folding opportunities. For example, it can be used in `MemorySessionImpl::checkValidStateRaw` to eliminate the lifetime check on global sessions without imposing additional branches on other non-global sessions. This is similar to `__builtin_constant_p` in GCC and clang.
>> 
>> Please kindly give your opinion as well as your reviews, thanks very much.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   ident

A few more stylistic comments :)

Still thinking the better home for these might be just `jdk.internal.misc.VM`... But I would not insist, if others are happy.

src/java.base/share/classes/jdk/internal/misc/JitCompiler.java line 56:

> 54:      */
> 55:     @IntrinsicCandidate
> 56:     public static boolean isCompileConstant(boolean expr) {

Here and in other places: probably not `expr`, but just `val` or something?

src/java.base/share/classes/jdk/internal/misc/JitCompiler.java line 119:

> 117:      * @see #isCompileConstant(boolean)
> 118:      */
> 119:     @IntrinsicCandidate

Note how the Java entry for MH intrinsic we have replaced had `@Hidden`. These methods should have `@Hidden` too then? Probably applies to other entries too.

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PR Review: https://git.openjdk.org/jdk/pull/17527#pullrequestreview-1839475907
PR Review Comment: https://git.openjdk.org/jdk/pull/17527#discussion_r1463705907
PR Review Comment: https://git.openjdk.org/jdk/pull/17527#discussion_r1463703771